Radio communication base station device, radio communication mobile station device, and control channel allocation method

ABSTRACT

Provided is a radio communication station device which can prevent limiting of resource allocation in a UE group. The radio communication device includes: a CCE allocation unit ( 104 ); modulation units ( 103 - 1  to  103 -K); an arrangement unit ( 108 ); and a radio transmission unit ( 111 ). The CCE allocation unit ( 104 ) allocates allocation information allocated to a PDCCH which is inputted from the modulation unit ( 103 - 1  to  103 -K) as follows. Among a plurality of search spaces shared by a greater number of UE groups as the CCE aggregation size of the PDCCH increases, a particular search space corresponding to the CCE aggregation size of the PDCCH and a mobile group (UE group) of the PDCCH is selected as a space to which the allocation information is to be allocated. The arrangement unit ( 108 ) arranges the allocation information in a downlink resource corresponding to the CCE of the particular search space allocated among the downlink resources secured for the PDCCH. The radio transmission unit ( 111 ) transmits an OFDM symbol having the allocation information from an antenna ( 112 ) to a mobile station.

TECHNICAL FIELD

The present invention relates to a radio communication base stationapparatus, radio communication mobile station apparatus and controlchannel allocating method.

BACKGROUND ART

In mobile communication, a radio communication base station apparatus(hereinafter abbreviated as “base station”) transmits controlinformation for reporting a resource allocation result of downlink dataand uplink data, to radio communication mobile station apparatuses(hereinafter abbreviated as “mobile stations”). This control informationis transmitted to the mobile stations using downlink control channelssuch as a PDCCH (Physical Downlink Control CHannel). Each PDCCH occupiesone or a plurality of consecutive CCE's (Control Channel Elements). Thebase station generates PDCCH's on a per mobile station basis, allocatesCCE's to be occupied to the PDCCH's according to the number of CCE'srequired for control information, maps the control information on thephysical resources associated with the allocated CCE's, and transmitsthe results.

For example, in order to satisfy the desired received quality, an MCS(Modulation and Coding Scheme) of a low MCS level needs to be set for amobile station that is located near the cell boundary of poor channelquality. Therefore, the base station transmits a PDCCH that occupies alarger number of CCE's (e.g. eight CCE's). By contrast, even if an MSCof a high MCS level is set for a mobile station that is located near thecenter of a cell of good channel quality, it is possible to satisfy thedesired received quality. Therefore, the base station transmits a PDCCHthat occupies a smaller number of CCE's (e.g. one CCE). Here, the numberof CCE's occupied by one PDCCH (i.e. CCE occupation number) is referredto as “CCE aggregation size.” For example, when the CCE aggregationsizes of 1, 2, 4 and 8 are used, a mobile station that is located nearthe cell center tries to receive a PDCCH of the CCE aggregation size of1, and a mobile station that is located near the cell edge tries toreceive a PDCCH of the CCE aggregation size of 8.

Also, a base station allocates a plurality of mobile stations to onesubframe and therefore transmits a plurality of PDCCH's at the sametime. In this case, the base station transmits control informationincluding CRC bits scrambled by the ID numbers of the destination mobilestations, so that the destination mobile station of each PDCCH can beidentified. Further, the mobile stations decode CCE's to which PDCCH'scan be arranged, and perform CRC detection after descrambling the CRCbits by their mobile station ID numbers. Thus, mobile stations detectthe PDCCH's for those mobile stations by performing blind decoding of aplurality of PDCCH's included in a received signal.

However, when the total number of CCE's is large, the number of times amobile station performs blind decoding increases. Therefore, in order toreduce the number of times a mobile station performs blind decoding, amethod of limiting the CCE's subject to blind decoding on a per mobilestation basis, is studied (see Non-Patent Document 1). With this method,a plurality of mobile stations are grouped, and CCE fields to includeCCE's subject to blind decoding are limited on a per group basis. Forexample, when a plurality of mobile stations are grouped into UE groups#1 to #4, among CCE's #0 to #31, four CCE fields of CCE's #0 to #7,CCE's #8 to 15, CCE's #16 to 23, and CCE's #24 to 31, are subject toblind decoding in the UE groups, respectively. By this means, the mobilestation of each UE group needs to perform blind decoding of only the CCEfield allocated to that mobile station, so that it is possible to reducethe number of times of blind decoding. Here, the CCE field subject toblind decoding by a mobile station is referred to as “search space.”

Also, in order to reduce the number of times a mobile station performsblind decoding, studies are underway on a method of limiting in advancethe starting location of CCE's occupied by the PDCCH of each CCEaggregation size (see Non-Patent Document 2). With this method, forexample, among CCE's #0 to #31, when the CCE aggregation size is 8, thestarting locations of CCE's (eight CCE's in this case) occupied byPDCCH's are limited to CCE #0, CCE #8, CCE #16 and CCE #24. By thismeans, each mobile station needs to perform blind decoding of PDCCH's ofa CCE aggregation size starting from the CCE starting locations, so thatit is possible to reduce the number of times of blind decoding.

-   Non-Patent Document 1: 3GPP RAN WG1 Meeting document, R1-073996,    “Search Space definition: Reduced PDCCH blind detection for split    PDCCH search space,” Motorola-   Non-Patent Document 2: 3GPP RAN WG1 #50bis, R1-074317, “Reducing the    decoding complexity of the PDCCH,” Nokia

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

As described in the above prior art, in a case where a plurality ofmobile stations are grouped into a plurality of UE groups and a searchspace is set on a per UE group basis, if a PDCCH of a larger CCEaggregation size is used in a UE group, it may not be able to allocate aPDCCH to other mobile stations. For example, among CCE's #0 to #31, in aUE group having a search space comprised of CCE's #0 to #7, if a PDCCHof a CCE aggregation size of 8 is allocated to a certain mobile station,CCE's #0 to #7 are all occupied, and therefore it is not possible toallocate a PDCCH to other mobile stations. Thus, resource allocation formobile stations in UE groups is limited, and, consequently, there is apossibility that large transmission delay occurs or control informationcannot be transmitted to a mobile station having good channel quality,which degrades the cell throughput.

It is therefore an object of the present invention to provide a radiocommunication base station apparatus, radio communication mobile stationapparatus and control channel allocating method for preventing resourceallocation in UE groups from being limited.

Means for Solving the Problem

The radio communication base station apparatus of the present inventionemploys a configuration having: an allocating section that allocates acontrol channel, which occupies one or a plurality of control channelelements, to a specific control channel element field associated with anumber of control channel elements occupied by the control channel and aUE group of the control channel, among a plurality of control channelelement fields shared by a larger number of user equipment groups whenthe number of control channel elements occupied by the control channelincreases; and a transmitting section that transmits the control channelallocated to the specific control channel element field.

Advantageous Effect of the Invention

According to the present invention, it is possible to prevent resourceallocation in UE groups from being limited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing the configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 2 is a block diagram showing the configuration of a mobile stationaccording to Embodiment 1 of the present invention;

FIG. 3 shows search spaces of allocating method 1 according toEmbodiment 1 of the present invention;

FIG. 4 shows search spaces of allocating method 2 according toEmbodiment 1 of the present invention;

FIG. 5 shows other search spaces of allocating method 2 according toEmbodiment 1 of the present invention;

FIG. 6 shows search spaces of allocating method 3 according toEmbodiment 1 of the present invention;

FIG. 7 shows search spaces of allocating method 4 according toEmbodiment 1 of the present invention;

FIG. 8 shows other search spaces according to Embodiment 1 of thepresent invention;

FIG. 9 shows search spaces according to Embodiment 2 of the presentinvention; and

FIG. 10 shows other search spaces according to Embodiment 2 of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained below in detailwith reference to the accompanying drawings. In the followingexplanation, assume that the total number of CCE's to which PDCCH's areallocated is 32, from CCE #0 to CCE #31, and the PDCCH CCE aggregationsize is one of 1, 2, 4 and 8. Also, if one PDCCH occupies a plurality ofCCE's, the plurality of CCE's occupied by the PDCCH are consecutive.

Also, in each CCE aggregation size, the starting location of CCE's towhich a PDCCH is allocated is set in advance. To be more specific, whenthe CCE aggregation size is 1, a PDCCH is allocated to one of CCE #0 toCCE #31. Also, when the CCE aggregation size is 2, a PDCCH is allocatedto two CCE's with starting locations of CCE #0, CCE #2, CCE #4, . . . ,CCE #28 and CCE #30. Similarly, when the CCE aggregation size is 4, aPDCCH is allocated to four CCE's with starting locations of CCE #0, CCE#4, CCE #8, CCE #12, CCE #16, . . . , CCE #24 and CCE #28, and, when theCCE aggregation size is 8, a PDCCH is allocated to eight CCE's withstarting locations of CCE #0, CCE #8, CCE #16 and CCE #24.

Also, in the following explanation, depending on the position of eachmobile station in a cell, the CCE aggregation size of a PDCCH to bereceived by that mobile station is determined. For example, a mobilestation that is located near the cell edge has poor channel quality andtherefore is likely to perform transmission with a lower MCS.Consequently, the CCE aggregation size for a mobile station that islocated near the cell edge is limited to 4 or 8. By contrast, a mobilestation that is located near the cell center has good channel qualityand therefore is likely to perform transmission with a higher MCS.Consequently, the CCE aggregation size for a mobile station that islocated neat the cell center is limited to 1 or 2. Each mobile stationmay determine the CCE aggregation size of a PDCCH to be received by thatmobile station, based on the location of that mobile station in a celldecided from received quality, and so on, or may be notified in advanceof the CCE aggregation size of a PDCCH to be received by that mobilestation.

Also, in the following explanation, mobile stations that are located ina cell are grouped into four mobile station groups (i.e. UE groups #1 to#4). Here, the mobile station groups to which mobile stations belong maybe reported per mobile station from a base station, or may be determinedimplicitly by a mobile station ID.

Also, assume that downlink data is transmitted by OFDM (OrthogonalFrequency Division Multiplexing), and uplink data is transmitted bySC-FDMA (Single-Carrier Frequency Division Multiple Access). Also,assume that a response signal transmitted in uplink is subjected to thefirst spreading by a ZAC (Zero Auto Correlation) sequence and secondspreading by a block-wise spreading code sequence.

Embodiment 1

FIG. 1 shows the configuration of base station 100 according to thepresent embodiment, and FIG. 2 shows the configuration of mobile station200 according to the present embodiment.

Here, to avoid complicated explanation, FIG. 1 shows componentsassociated with transmission of downlink data that is closely related tothe present invention and components associated with reception of uplinkresponse signals to that downlink data, and the illustration andexplanation of the components associated with reception of uplink datawill be omitted. Similarly, FIG. 2 shows components associated withreception of downlink data that is closely related to the presentinvention and components associated with transmission of uplink responsesignals to that downlink data, and the illustration and explanation ofthe components associated with transmission of uplink data will beomitted.

In base station 100 shown in FIG. 1, encoding section 101 receives asinput mobile station group information indicating the search spacedefinition of each mobile station group (i.e. UE groups #1 to #4).Further, encoding section encodes the mobile station group informationreceived as input, and outputs the result to modulating section 102.Next, modulating section 102 modulates the encoded mobile station groupinformation received as input from encoding section 101, and outputs theresult to arranging section 108.

Encoding and modulating sections 103-1 to 103-K receive as inputresource allocation information for uplink data or downlink datadirected to mobile stations. Here, each allocation information isallocated to a PDCCH of the CCE aggregation size required to transmitthat allocation information. Further, encoding and modulating sections103-1 to 103-K are provided in association with maximum K mobilestations #1 to #K. In encoding and modulating sections 103-1 to 103-K,encoding sections 11 each encode allocation information allocated toinput PDCCH's, and output the results to modulating sections 12. Next,modulating sections 12 each modulate the encoded allocation informationreceived as input from encoding sections 11, and output the results toCCE allocating section 104.

CCE allocating section 104 allocates the allocation information receivedas input from modulating sections 103-1 to 103-K, to one or a pluralityof CCE's based on mobile station group information. To be more specific,CCE allocating section 104 allocates a PDCCH to a specific search spaceassociated with the CCE aggregation size and mobile station group (“UEgroup”) of that PDCCH, among a plurality of search spaces which areshared by a larger number of UE groups when the PDCCH CCE aggregationsize increases. Further, CCE allocating section 104 outputs allocationinformation allocated to CCE's, to arranging section 108. Here, thePDCCH allocation processing in CCE allocating section 104 will bedescribed later in detail.

On the other hand, encoding section 105 encodes transmission data (i.e.downlink data) received as input, and outputs the result toretransmission control section 106. Here, if there are a plurality itemsof transmission data for a plurality of mobile stations, encodingsection 105 encodes each of the plurality items of transmission data forthese mobile stations.

Upon the initial transmission, retransmission control section 106 holdsand outputs encoded transmission data of each mobile station tomodulating section 107. Here, retransmission control section 106 holdstransmission data until an ACK from each mobile station is received asinput from deciding section 117. Further, if a NACK from each mobilestation is received as input from deciding section 117, that is, uponretransmission, retransmission control section 106 outputs transmissiondata associated with that NACK to modulating section 107.

Modulating section 107 modulates encoded transmission data received asinput from retransmission control section 106, and outputs the result toarranging section 108.

Arranging section 108 arranges allocation information to downlinkresources associated with allocated CCE's among downlink resourcessecured for PDCCH's, arranges mobile station group information todownlink resources secured for broadcast channels, and arrangestransmission data to downlink resources secured for transmission data.Further, arranging section 108 outputs signals to which those channelsare allocated, to IFFT (Inverse Fast Fourier Transform) section 109.

IFFT section 109 generates an OFDM symbol by performing an IFFT of aplurality of subcarriers to which allocation information, mobile stationgroup information or transmission data is allocated, and outputs theresult to CP (Cyclic Prefix) attaching section 110.

CP attaching section 110 attaches the same signal as the signal at thetail end part of the OFDM symbol, to the head of that OFDM symbol, as aCP.

Radio transmitting section 111 performs transmission processing such asD/A conversion, amplification and up-conversion on the OFDM symbol witha CP, and transmits the result from antenna 112 to mobile station 200(in FIG. 2).

On the other hand, radio receiving section 113 receives a SC-FDMA symboltransmitted from each mobile station, via antenna 112, and performsreceiving processing such as down-conversion and A/D conversion on thisSC-FDMA symbol.

CP removing section 114 removes the CP attached to the SC-FDMA symbolsubjected to receiving processing.

Despreading section 115 despreads a response signal by the block-wisespreading code sequence used in second spreading in mobile station 200,and outputs the despread response signal to correlation processingsection 116.

Correlation processing section 116 finds the correlation value betweenthe despread response signal and the ZAC sequence used in the firstspreading in mobile station 200, and outputs the correlation value todeciding section 117.

Deciding section 117 detects a response signal per mobile station bydetecting the correlation peak of each mobile station in a detectionwindow. For example, upon detecting a correlation peak in detectionwindow #0 for mobile station #0, deciding section 117 detects a responsesignal from mobile station #0. Further, deciding section 117 decideswhether the detected response signal is an ACK or NACK, bysynchronization detection using the correlation value of a referencesignal, and outputs an ACK or NACK to retransmission control section 106on a per mobile station basis.

On the other hand, mobile station 200 shown in FIG. 2 receives mobilestation group information, allocation information and downlink datatransmitted from base station 100. The method of receiving these itemsof information will be explained below.

In mobile station 200 shown in FIG. 2, radio receiving section 202receives an OFDM symbol transmitted from base station 100 (in FIG. 1),via antenna 201, and performs receiving processing such asdown-conversion and A/D conversion on the OFDM symbol.

CP removing section 203 removes the CP attached to the OFDM symbolsubjected to receiving processing.

FFT (Fast Fourier Transform) section 204 performs an FFT of the OFDMsymbol to acquire allocation information, broadcast informationincluding mobile station group information, and downlink data, which aremapped on a plurality of subcarriers, and outputs the results toseparating section 205.

Separating section 205 separates broadcast information arranged toresources secured in advance for broadcast channels, from signalsreceived as input from FFT section 204, outputs the broadcastinformation to broadcast information decoding section 206 and outputsinformation other than the broadcast information to extracting section207.

Broadcast information decoding section 206 decodes the broadcastinformation received as input from separating section 205 to acquiremobile station group information, and outputs the mobile station groupinformation to extracting section 207.

Assume that extracting section 207 and decoding section 209 receive inadvance coding rate information indicating the coding rate of allocationinformation, that is, information indicating the PDCCH CCE aggregationsize. Here, information indicating the PDCCH CCE aggregation size may bedesignated from base station 100 or may be determined by mobile station200 based on the received quality of pilot signals.

Also, upon receiving allocation information, extracting section 207extracts allocation information subject to blind decoding from theplurality of subcarriers, according to the search space of a mobilestation group to which the subject mobile station belongs, designated bythe CCE aggregation size and mobile station group information receivedas input, and outputs the allocation information to demodulating section208.

Demodulating section 208 demodulates the allocation information andoutputs the result to decoding section 209.

Decoding section 209 decodes the allocation information according to theCCE aggregation size received as input, and outputs the result todeciding section 210.

On the other hand, upon receiving downlink data, extracting section 207extracts downlink data for the subject mobile station from the pluralityof subcarriers, according to a resource allocation result received asinput from deciding section 210, and outputs the downlink data todemodulating section 212. This downlink data is demodulated indemodulating section 212, decoded in decoding section 213 and receivedas input in CRC section 214.

CRC section 214 performs an error detection of the decoded downlink datausing CRC, generates an ACK in the case of CRC=OK (no error) or a NACKin the case of CRC=NG (error present), as a response signal, and outputsthe generated response signal to modulating section 215. Further, in theease of CRC=OK (no error), CRC section 214 outputs the decoded downlinkdata as received data.

Deciding section 210 performs a blind detection as to whether or not theallocation information received as input from decoding section 209 isdirected to the subject mobile station. To be more specific, against theallocation information received as input from decoding section 209,deciding section 210 performs a blind detection as to whether or not theallocation information is directed to the subject mobile station. Forexample, if CRC=OK is found (i.e. no error is found) as a result ofdemasking CRC bits by the ID number of the subject mobile station,deciding section 210 decides that allocation information is directed tothat mobile station. Further, deciding section 210 outputs theallocation information directed to the subject mobile station, that is,the resource allocation result of downlink data for that mobile station,to extracting section 207.

Further, deciding section 210 decides a PUCCH (Physical Uplink ControlCHannel) to use to transmit a response signal from the subject mobilestation, from the CCE number associated with a subcarrier to which aPDCCH allocated the allocation information for that mobile station isarranged. Further, deciding section 210 outputs the decision result(i.e. PUCCH number) to control section 211. That is, the PUCCH number isderived from the CCE number used in a PDCCH used for data allocation.For example, if the CCE associated with a subcarrier to which a PDCCHdirected to the subject mobile station is arranged is CCE #0, decidingsection 210 decides that PUCCH #0 associated with CCE #0 is the PUCCHfor that mobile station. Also, for example, if the CCE's associated withsubcarriers to which a PDCCH directed to the subject mobile station isarranged are CCE #0 to CCE #3, deciding section 210 decides that PUCCH#0 associated with CCE #0 of the minimum number among CCE #0 to CCE #3,is the PUCCH for that mobile station.

Based on the PUCCH number received as input from deciding section 210,control section 211 controls the cyclic shift value of the ZAC sequenceused in the first spreading in spreading section 216 and the block-wisespreading code sequence which is used in second spreading in spreadingsection 219 and which is the spreading code sequence used in spreadingper LB (Long Block). For example, control section 211 selects the ZACsequence of the cyclic shift value associated with the PUCCH numberreceived as input from deciding section 210, from among twelve ZAC'sfrom ZAC #0 to ZAC #11, and sets the ZAC sequence in spreading section216, and selects the block-wise spreading code sequence associated withthe PUCCH number received as input from deciding section 210, from amongthree block-wise spreading code sequences from BW #0 to BW #2, and setsthe block-wise spreading code sequence in spreading section 219. Thatis, control section 211 selects one of a plurality of resources definedby ZAC #0 to ZAC #11 and by BW #0 to BW #2.

Modulating section 215 modulates a response signal received as inputfrom CRC section 214 and outputs the result to spreading section 216.

Spreading section 216 performs first spreading of the response signal bythe ZAC sequence set in control section 211, and outputs the responsesignal subjected to the first spreading to IFFT section 217. That is,spreading section 216 performs the first spreading of the responsesignal using the ZAC sequence of the cyclic shift value associated withthe resource selected in control section 211. Here, in the firstspreading, it is equally possible to use sequences that can be separatedfrom each other by varying cyclic shift values, other than ZACsequences. For example, in the first spreading, it is equally possibleto use GCL (Generalized Chirp Like) sequences, CAZAC (Constant AmplitudeZero Auto Correlation) sequences, ZC (Zadoff-Chu) sequences, or use PNsequences such as M sequences and orthogonal Gold code sequences.

IFFT section 217 performs an IFFT of the response signal subjected tothe first spreading, and outputs the response signal subjected to anIFFT to CP attaching section 218.

CP attaching section 218 attaches the same signal as the tail end partof the response signal subjected to an IFFT, to the head of thatresponse signal as a CP.

Spreading section 219 performs second spreading of the response signalwith a CP by the block-wise spreading code sequence set in controlsection 211, and outputs the response signal subjected to secondspreading to radio transmitting section 220. Here, in second spreading,as block-wise spreading code sequences, it is possible to use anysequences as long as these sequences can be regarded as sequences thatare orthogonal or substantially orthogonal to each other. For example,in second spreading, it is possible to use Walsh sequences or Fouriersequences as block-wise spreading code sequences.

Radio transmitting section 220 performs transmission processing such asD/A conversion, amplification and up-conversion on the response signalsubjected to second spreading, and transmits the result from antenna 201to base station 100 (in FIG. 1).

Next, CCE allocating methods 1 to 4 in CCE allocating section 104 willbe explained in detail.

<Allocating Method 1 (in FIG. 3)>

With the present allocating method, a PDCCH is allocated to a specificsearch space associated with the CCE aggregation size and mobile stationgroup of that PDCCH, among a plurality of search spaces shared by alarger number of UE groups when the CCE aggregation size increases.

To be more specific, when the CCE aggregation size is 1, as shown inFIG. 3, the search space of UE group #1 is formed with eight CCE's fromCCE #0 to CCE #7, the search space of UE group #2 is formed with eightCCE's from CCE #8 to CCE #15, the search space of UE group #3 is formedwith eight CCE's from CCE #16 to CCE #23, and the search space of UEgroup #4 is formed with eight CCE's from CCE #24 to CCE #31.

Also, when the CCE aggregation size is 2, as shown in FIG. 3, the searchspace of UE groups #1 and #2 is formed with sixteen CCE's from CCE #0 toCCE #15, and the search space of UE groups #3 and #4 is formed withsixteen CCE's from CCE #16 to CCE #31.

Also, when the CCE aggregation size is 4 or 8, as shown in FIG. 3, thesearch space of UE groups #1 to #4 is formed with thirty-two CCE's fromCCE #0 to CCE #31, that is, all CCE's.

When the CCE aggregation size increases, the number of UE groups thatshare one search space increases. To be more specific, referring to CCE#0, CCE #0 is used only by UE group #1 when the CCE aggregation size is1, used by two UE groups #1 and #2 when the CCE aggregation size is 2,and used by all UE groups #1 to #4 when the CCE aggregation size is 4 or8. Also, when the CCE aggregation size is maximum 8, the search space isshared by all UE groups, and, when the CCE aggregation size is minimum1, the search space of each UE group varies between UE groups.

Also, when the CCE aggregation size increases, the search spaceassociated with each UE group increases. To be more specific, referringto UE group #1, the search space of UE group #1 is formed with eightCCE's when the CCE aggregation size is 1, formed with sixteen CCE's whenthe CCE aggregation size is 2, and formed with thirty-two CCE's when theCCE aggregation size is 4 or 8.

Therefore, as shown in FIG. 3, with respect to the mobile stations of UEgroup #1, CCE allocating section 104 can allocate maximum eight PDCCH'sof a CCE aggregation size of 1 to the search space from CCE #0 to CCE#7, and allocate maximum eight PDCCH's of a CCE aggregation size of 2 tothe search space from CCE #0 to #15. Similarly, CCE allocating section104 can allocate maximum eight PDCCH's of a CCE aggregation size of 4 tothe search space from CCE #0 to CCE #31, and allocate maximum fourPDCCH's of a CCE aggregation size of 8.

By this means, CCE allocating section 104 relaxes the allocationrestriction for a mobile station to which a PDCCH of a larger CCEaggregation size is allocated. For example, a case will be explainedwhere CCE allocating section 104 allocates a PDCCH of a CCE aggregationsize of 1 and PDCCH of a CCE aggregation size of 8 for UE group #1.Also, in this case, assume that there are no mobile stations to which aPDCCH of a CCE aggregation size of 1 for UE group #2 is allocated.

Upon allocating PDCCH's to CCE's, CCE allocating section 104 allocates aPDCCH of a CCE aggregation size of 8, avoiding allocation of this PDCCHto the same CCE's as those for a PDCCH of a smaller CCE aggregationsize, 1. To be more specific, avoiding the search space of UE group #1from CCE #0 to CCE #7 of a CCE aggregation size of 1, CCE allocatingsection 104 allocates a PDCCH of a CCE aggregation size of 8. Here,there are no mobile stations to which a PDCCH of a CCE aggregation sizeof 1 for UE group #2 (where the search space ranges from CCE #8 to CCE#15) is allocated, so that CCE allocating section 104 allocates a PDCCHof a CCE aggregation size of 8 to CCE #8 to CCE #15. Further, CCEallocating section 104 allocates a PDCCH of a CCE aggregation size of 1for UE group #1 to one of CCE #0 to CCE #7.

Thus, in base station 100, when the CCE aggregation size increases, alarger number of UE groups share search spaces. Therefore, when the CCEaggregation size increases, it is possible to allocate a PDCCH to CCE'sof a wider range. By this means, even if PDCCH's of varying CCEaggregation sizes are allocated in the same UE group, by adjusting CCEallocation for a PDCCH of a larger CCE aggregation size, base station100 can allocate these PDCCH's without limiting resource allocation.

On the other hand, mobile station 200 demodulates, decodes and performsblind detection of a PDCCH based on the CCE aggregation size and mobilestation group information. For example, when mobile station 200belonging to UE group #1 performs blind detection on the presumptionthat the CCE aggregation size is 1, extracting section 207 outputs onlysignals associated with CCE #0 to CCE #7, among CCE #0 to CCE #31 shownin FIG. 3, to demodulating section 208. That is, in demodulating section208, decoding section 209 and deciding section 210, the target for blinddetection in a case where the CCE aggregation size is 1, is limited tothe search space corresponding to CCE #0 to CCE #7. Similarly, uponperforming blind detection on the presumption that the CCE aggregationsize is 2, extracting section 207 outputs only signals associated withCCE #0 to CCE #15, among CCE #0 to CCE #31 shown in FIG. 3, todemodulating section 208. Also, if it is presumed that the CCEaggregation size is 4 or 8, extracting section 207 outputs signalsassociated with CCE #0 to CCE #31 shown in FIG. 3, that is, signalsassociated with all CCE's, to demodulating section 208.

Here, when the CCE aggregation size is 1, the number of PDCCH'sallocated to the eight CCE's in each of UE groups #1 to #4 is eight.Also, when the CCE aggregation size is 2, the number of PDCCH'sallocated to the sixteen CCE's of UE groups #1, #2, #3 and #4 is eight.On the other hand, the number of PDCCH's allocated to CCE #0 to CCE #31is eight when the CCE aggregation size is 4, or four when the CCEaggregation size is 8. That is, even in a case where the search space isformed with all CCE's from CCE #0 to CCE #31 when the CCE aggregationsize is 4 or 8, compared to a case where the CCE aggregation size is 1or 2, the number of PDCCH's subject to blind detection does notincrease.

Also, the CCE aggregation size is determined based on the location of amobile station in a cell or received quality. Therefore, the systemperformance is hardly influenced by the degradation of freedom degree ofCCE allocation caused by limiting the CCE aggregation size of a receivedPDCCH on a per mobile station basis.

Also, the search space of each UE group is formed with consecutiveCCE's, and, consequently, upon reporting a search space from a basestation to a mobile station, the base station only needs to report thehead CCE number and the end CCE number, so that it is possible to reducethe amount of report information.

Thus, according to this allocation example, a PDCCH is allocated to oneof a plurality of search spaces shared by a larger number of UE's whenthe CCE aggregation size increases. By this means, a base station canallocate a PDCCH of a larger CCE aggregation size to CCE's such thatthese CCE's do not overlap with CCE's used for a PDCCH of a smaller CCEaggregation size. Therefore, with the present allocating method, it ispossible to prevent resource allocation in UE groups from being limitedwithout increasing the number of times of blind decoding.

<Allocating Method 2 (in FIG. 4)>

In the search spaces of allocating method 1 shown in FIG. 3, if at leastone PDCCH of a CCE aggregation size of 8 for a given UE group is used,it is not possible to use any of PDCCH's of a CCE aggregation size of 1for UE groups #1 to #4.

For example, in the search spaces shown in FIG. 3, assume that a PDCCHof a CCE aggregation size of 8 is used in CCE #0 to CCE #7. Here, asshown in FIG. 3, a PDCCH of a CCE aggregation size of 1 for UE group #1is allocated to one of CCE #0 to CCE #7. However, CCE #0 to CCE #7 arealready used by the PDCCH of a CCE aggregation size of 8, and,consequently, a base station cannot allocate the PDCCH of a CCEaggregation size of 1 for UE group #1. Also, similarly, when a PDCCH ofa CCE aggregation size of 8 is allocated to CCE #8 to CCE #15, CCE #16to CCE #23 or CCE #24 to CCE #31, it is not possible to use any ofPDCCH's of a CCE aggregation size of 1 for UE groups #2 to #3.

Therefore, CCE allocating section 104 according to the presentallocating method allocates a PDCCH to a specific search space formedwith CCE's occupied by a plurality of PDCCH's of a larger CCEaggregation size than the CCE aggregation size of that PDCCH.

To be more specific, when the CCE aggregation size is 1, as shown inFIG. 4, the search space of UE group #1 is formed with eight CCE's fromCCE #0 to CCE #3 and CCE #16 to CCE #19, and the search space of UEgroup #2 is formed with eight CCE's from CCE #4 to CCE #7 and CCE #20 toCCE #23. Similarly, the search space of UE group #3 is formed with eightCCE's from CCE #8 to CCE #11 and CCE #24 to CCE #27, and the searchspace of UE group #4 is formed with eight CCE's from CCE #12 to CCE #15and CCE #28 to CCE #31.

Also, as shown in FIG. 4, the search spaces of CCE aggregation sizes of2, 4 and 8 are formed in the same way as in allocating method 1 (in FIG.3).

That is, the search spaces of a CCE aggregation size of 1 for UE groups#1 to #4 are separately arranged into two different PDCCH units amongfour PDCCH units (CCE #0 to CCE #7, CCE #8 to CCE #15, CCE #16 to CCE#23 and CCE #24 to CCE #31) to which a PDCCH of a CCE aggregation sizeof 8 is allocated. For example, the search space of a CCE aggregationsize of 1 for UE group #1 (CCE #0 to CCE #3 and CCE #16 and CCE #19) isformed with CCE's included in two different PDCCH's of a CCE aggregationsize of 8 (CCE #0 to CCE #7 and CCE #16 and CCE #23).

By this means, even in a case where a PDCCH of a CCE aggregation size of8 is allocated to any of CCE #0 to CCE #31, if it is not possible to useone of search spaces separately arranged, it is possible to allocate aPDCCH to the other search space.

For example, in the search spaces shown in FIG. 4, assume that CCEallocating section 104 allocates a PDCCH of a CCE aggregation size of 8for a given UE group, to CCE #0 to CCE ∩7. Here, in a case where a PDCCHof a CCE aggregation size of 1 for UE group #1 is further allocated, asshown in FIG. 4, CCE #0 to CCE #7 are already used, and therefore CCEallocating section 104 cannot allocate that PDCCH to CCE #0 to CCE #3,which form one of the search spaces of a CCE aggregation size of 1 forUE group #1. However, CCE #16 to CCE #19, which form the other searchspace of a CCE aggregation size of 1 for UE group #1, are not used, sothat CCE allocating section 104 can allocate a PDCCH of a CCEaggregation size of 1 for UE group #1 to one of CCE #16 to CCE #19.

Thus, according to the present allocating method, a PDCCH is allocatedto a specific search space formed with CCE's occupied by a plurality ofPDCCH's of a larger CCE aggregation size than the CCE aggregation sizeof that PDCCH. That is, a base station allocates a PDCCH to specificsearch spaces separately arranged into different CCE's. By this means,even if PDCCH's of different CCE aggregation sizes are used at the sametime, a PDCCH of a smaller CCE aggregation size can use any of CCE'sseparately arranged. Therefore, with the present allocating method, itis possible to further prevent resource allocation in UE groups frombeing limited.

Also, with the present allocating method, as shown in FIG. 5, the searchspaces of a smaller CCE aggregation size for UE groups may be evenlyincluded in each PDCCH unit of a larger CCE aggregation size. To be morespecific, as shown in FIG. 5, for example, two search spaces of a CCEaggregation size of 1 for each of UE groups #1 to #4 may be included ineach PDCCH unit of a CCE aggregation size of 8 (CCE #0 to CCE #7, CCE #8to CCE #15, CCE #16 to CCE #23 and CCE #24 to CCE #31). Similarly, twosearch spaces of a CCE aggregation size of 2 for UE groups #1 and #2 andtwo search spaces of a CCE aggregation size of 2 for UE groups #3 and #4may be included in each PDCCH unit of a CCE aggregation size of 8. Thatis, search spaces of CCE aggregation sizes of 1 and 2 for UE groups areseparately arranged into four PDCCH units of a CCE aggregation size of8. By this means, even in a case where a PDCCH of a larger CCEaggregation size is allocated to given CCE's, as in the presentallocating method, it is possible to allocate a PDCCH of a smaller CCEaggregation size to any of CCE #0 to CCE #31, without limiting resourceallocation.

<Allocating Method 3 (in FIG. 6)>

With the present allocating method, a case will be explained where eachmobile station performs blind decoding in search spaces of a pluralityof CCE aggregation sizes. For example, a mobile station that is locatednear the cell center performs blind decoding in search spaces of CCEaggregation sizes of 1 and 2. Also, a mobile station that is locatednear the cell edge performs blind decoding in search spaces of CCEaggregation sizes of 4 and 8. Also, a mobile station that is locatedbetween the cell center and the cell edge performs blind decoding insearch spaces of CCE aggregation sizes of 2 and 4.

In this case, if PDCCH's of a plurality of different CCE aggregationsizes for the same UE group are used in the search spaces of allocatingmethod 1 shown in FIG. 3, the use of PDCCH's of a CCE aggregation sizeof 1 or 2 may be limited.

For example, in the search spaces shown in FIG. 3, assume that a PDCCHof a CCE aggregation size of 8 for UE group #1 (CCE #0 to CCE #7) isused. Here, as shown in FIG. 3, the search space of UE group #1 isformed with CCE #0 to CCE #7 when the CCE aggregation size is 1, and thesearch space of UE group #1 (shared by UE group #2) is formed with CCE#0 to CCE #15 when the CCE aggregation size is 2. That is, the searchspaces of CCE aggregation sizes of 1 and 2 are formed using overlappingCCE #0 to CCE #7. Therefore, all CCE's from CCE #0 to CCE #7 are alreadyused by a PDCCH of a CCE aggregation size of 8, and, consequently, abase station cannot allocate a PDCCH of a CCE aggregation size of 1 forUE group #1, and can allocate a PDCCH of a CCE aggregation size of 2 forUE group #1 only to CCE #8 to CCE #15.

Therefore, CCE allocating section 104 according to the presentallocating method allocates a PDCCH to a specific search space, among aplurality of search spaces formed with varying CCE's of varying CCEaggregation sizes in the same UE group.

To be more specific, when the CCE aggregation size is 1, as shown inFIG. 6, the search space of UE group #1 is formed with eight CCE's fromCCE #16 to CCE #23, and the search space of UE group #2 is formed witheight CCE's from CCE #24 to CCE #31. Also, the search space of UE group#3 is formed with eight CCE's from CCE #0 to CCE #7, and the searchspace of UE group #4 is formed with eight CCE's from CCE #8 to CCE #15.

Also, as shown in FIG. 6, search spaces of CCE aggregation sizes of 2, 4and 8 are formed in the same way as in allocating method 1 (in FIG. 3).

That is, in the same UE group, a search space of a CCE aggregation sizeof 1 for each UE group is formed with different CCE's from a searchspace of a CCE aggregation size of 2. For example, the search space of aCCE aggregation size of 1 for UE group #1 (CCE #16 to CCE #23) and thesearch space of a CCE aggregation size of 1 for UE group #2 (CCE #24 toCCE #31) are formed with different CCE's from the search space of a CCEaggregation size of 2 for UE groups #1 and #2 (CCE #0 to CCE #15). Thesame applies to UE groups #3 and #4.

By this means, the selection range of CCE's forming search spaces withCCE aggregation sizes of 1 and 2 is wider than in allocating method 1(in FIG. 3), and, consequently, resource allocation for mobile stationsto which PDCCH's of CCE aggregation sizes of 1 and 2 are allocated (i.e.mobile stations near the cell center) becomes flexible. For example,assume that a PDCCH of a CCE aggregation size of 8 (i.e. a PDCCHdirected to a mobile station near the cell edge) is allocated to CCE #0to CCE #7. In this case, CCE allocating section 104 cannot allocate aPDCCH of a CCE aggregation size of 1 or 2 for UE group #1 (i.e. a PDCCHdirected to a mobile station near the cell center) to CCE #0 to CCE #7.However, CCE allocating section 104 can allocate a PDCCH of a CCEaggregation size of 2 to CCE #8 to CCE #15 and allocate a PDCCH of a CCEaggregation size of 1 to CCE #16 to CCE #23. That is, according to thepresent allocating method, by forming search spaces of smaller CCEaggregation sizes with non-overlapping CCE's, CCE allocating section 104can flexibly allocate PDCCH's of smaller CCE aggregation sizes of 1 and2.

Thus, according to the present allocating method, a PDCCH is allocatedto a specific search space, among a plurality of search spaces formedwith varying CCE's of varying CCE aggregation sizes in the same UEgroup. By this means, the selection range of search spaces of smallerCCE aggregation sizes is wider than in allocating method 1. By thismeans, even if a PDCCH of a larger CCE aggregation size is used, it ispossible to flexibly allocate PDCCH's of smaller CCE aggregation sizes.Therefore, with the present allocating method, even if each mobilestation performs blind decoding in search spaces of a plurality of CCEaggregation sizes, it is possible to prevent resource allocation in UEgroups from being limited.

<Allocating Method 4 (in FIG. 7)>

Upon associating the CCE numbers used in uplink resource allocation andthe PUCCH numbers for transmitting a response signal, a mobile stationdecides that the PUCCH, which is associated with the CCE of the minimumnumber among one or a plurality of CCE's forming the PDCCH to whichallocation information for that mobile station is arranged, is the PUCCHfor that mobile station. Therefore, if all CCE's (e.g. CCE #0 to CCE#31) are associated with PUCCH's on a one-to-one basis, the amount ofresources for use becomes enormous.

Therefore, CCE allocating section 104 according to the presentallocating method allocates a PDCCH to a specific search space, among aplurality of search spaces formed with a smaller number of CCE's whenthe CCE aggregation size is smaller.

To be more specific, when the CCE aggregation size is 1, as shown inFIG. 7, the search spaces of UE groups #1 and #2 are formed with eightCCE's from CCE #16 to CCE #23, and the search spaces of UE groups #3 and#4 are formed with eight CCE's from CCE #24 to CCE #31. Also, when theCCE aggregation size is 2, the search spaces of UE groups #1 to #4 areformed with sixteen CCE's from CCE #16 to CCE #31. Also, as shown inFIG. 7, the search spaces of CCE aggregation sizes of 4 and 8 are formedin the same way as in allocating method 1 (in FIG. 3).

Therefore, in the case of a smaller CCE aggregation size of 1 or 2, thesearch spaces of UE groups #1 to #4 are formed with sixteen CCE's, whichare half of thirty-two CCE's from CCE #0 to CCE #31. That is, as shownin FIG. 7, when the CCE aggregation size is 1 or 2, CCE #0 to CCE #15are not used.

As above, CCE #0 to CCE #15 shown in FIG. 7 are used only for PDCCH's ofCCE aggregation sizes of 4 and 8. Therefore, upon allocating a PDCCH ofa CCE aggregation size of 4 or 8, CCE allocating section 104preferentially uses CCE #0 to CCE #15. By this means, CCE allocatingsection 104 can allocate PDCCH's of CCE aggregation sizes of 1 and 2 tosearch spaces of CCE #16 to CCE #31, without limiting resourceallocation.

Also, PDCCH's of CCE aggregation sizes of 1 and 2 are not used in thesearch spaces of CCE #0 to CCE #15 shown in FIG. 7, so that, among theCCE's forming each PDCCH of CCE aggregation sizes of 4 and 8, a resourcefor only the PUCCH associated with the CCE of the minimum number issecured. That is, as shown in FIG. 7, resources for four PUCCH'srespectively associated with four CCE's (CCE #0, CCE #4, CCE #8 and CCE#12) are secured. Therefore, among fifteen CCE's from CCE #0 to CCE #15,it is necessary to secure resources only for PUCCH's associated with thefour CCE's. Also, PDCCH's of CCE aggregation sizes of 1 and 2 are usedin CCE #16 to CCE #31, and therefore resources for sixteen PUCCH'srespectively associated with sixteen CCE's from CCE #16 to CCE #31 aresecured. Thus, by limiting the number of CCE's forming search spaces ofsmaller CCE aggregation sizes, it is possible to reduce the amount ofresources to secure for PUCCH's associated with CCE's.

Thus, according to the present allocating method, as in allocatingmethod 1, it is possible to allocate PDCCH's of smaller CCE aggregationsizes to CCE's without limiting resource allocation, and further reducethe amount of resources to secure for PUCCH's associated with CCE's.

Also, with the present allocating method, it is equally possible toswitch the definition of search spaces in a semi-static manner,depending on the amount of traffics. For example, it is possible to usethe definition of search spaces according to the present allocatingmethod (in FIG. 7) when the amount of traffics is low, or use, forexample, the definition of search spaces according to allocating method3 (in FIG. 6) when the amount of traffics is high. By this means, it ispossible to secure the amount of resources for PUCCH's associated withCCE's, without loss.

Also, a case has been described with the present allocating method wheresearch spaces of CCE aggregation sizes of 1 and 2 are formed with CCE#16 to CCE #31. However, with the present allocating method, it isequally possible to form search spaces of CCE aggregations of 1 and 2with CCE #0 to CCE #15.

Also, although a case has been described above with the presentallocating method where CCE's and PUCCH's (i.e. response signals todownlink data) are associated, even if CCE's and PHICH's (physicalhybrid ARQ indicator channels) are associated, the present invention canprovide the same effect as above. Here, response signals to uplink dataare allocated to PHICH's.

Also, a PUCCH used in the explanation of the present allocating methodis a channel for feeding back an ACK or NACK, and therefore can bereferred to as “ACK/NACK channel.”

Also, even in a case where control information other than responsesignals is fed back, the present invention can be implemented as above.

Allocating methods 1 to 4 of PDCCH's according to the present embodimenthave been described above.

Thus, according to the present embodiment, a PDCCH of a larger CCEaggregation size can flexibly use CCE's such that these CCE's do notoverlap with CCE's allocated to a PDCCH of a smaller CCE aggregationsize. Therefore, according to the present embodiment, it is possible toprevent resource allocation in UE groups from being limited.

Also, with the present embodiment, it is equally possible to form searchspaces by combining above allocating methods 1 to 4. For example, FIG. 8shows search spaces acquired by combining allocating methods 2 and 3.Here, as shown in FIG. 8, in a case where the CCE aggregation size is 4,the search spaces of UE groups #1 and #2 are formed with CCE #0 to CCE#15, and the search spaces of UE groups #3 and #4 are formed with CCE#16 to CCE #31. In this case, as in allocating method 2, the searchspaces of a CCE aggregation size of 2 for each UE group are separatelyarranged such that these search spaces are included in two search spacesof a CCE aggregation size of 4. Also, as in allocating method 2, thesearch spaces of a CCE aggregation size of 1 are separately arrangedinto CCE's occupied by varying PDCCH's of a larger CCE aggregation size.Further, as in allocating method 3, part of the search spaces of a CCEaggregation size of 1 is formed with different CCE's from search spacesof varying CCE aggregation sizes in the same UE group. For example, oneof search spaces of a CCE aggregation size of 1 for UE group #1 (e.g.CCE #0 to CCE #3) overlaps with a search space of a CCE aggregation sizeof 2 (CCE #0 to CCE #8). However, the other search space (e.g. CCE #24to CCE #27) does not overlap with any of the search spaces of a CCEaggregation size of 2 (CCE #0 to CCE #8 and CCE #16 to CCE #23). By thismeans, it is possible to provide the same advantage as in allocatingmethods 2 and 3 according to the present embodiment.

Embodiment 2

With the present embodiment, search spaces of varying CCE aggregationsizes of each UE group are formed with varying CCE's.

In the following explanation, the search space of each CCE aggregationsize for UE groups #1 to #4 is formed with eight CCE's. To be morespecific, as shown in FIG. 9, in UE group #1, the search space of a CCEaggregation size of 1 is formed with eight CCE's from CCE #24 to CCE#31, the search space of a CCE aggregation size of 2 is formed witheight CCE's from CCE #16 to CCE #23, the search space of a CCEaggregation size of 4 is formed with eight CCE's from CCE #8 to CCE #15,and the search space of a CCE aggregation size of 8 is formed with eightCCE's from CCE #0 to CCE #7. As shown in FIG. 9, the same applies to UEgroups #2 to #4.

That is, as shown in FIG. 9, the search spaces of CCE aggregation sizesof 1, 2, 4 and 8 for each UE group are formed with varying CCE's overentire CCE #0 to CCE #31. By this means, even in a case where a PDCCH ofa larger CCE aggregation size (e.g. a PDCCH of a CCE aggregation size of8) is used, CCE allocating section 104 can allocate PDCCH's of smallerCCE aggregation sizes reliably. That is, in the same UE group, even in acase where a PDCCH of a larger CCE aggregation size is used, there is nopossibility that a PDCCH of a smaller CCE aggregation size cannot beallocated. Also, in the same way as in allocating method 3 of Embodiment1, search spaces of varying CCE aggregation sizes are formed withvarying CCE's. Therefore, even in a case where each mobile stationperforms blind decoding in search spaces of a plurality of CCEaggregation sizes, in the same way as in allocating method 3 ofEmbodiment 1, CCE allocating section 104 can flexibly allocate a PDCCHto more CCE's without using overlapping CCE's.

Thus, according to the present embodiment, search spaces of varying CCEaggregation sizes in the same UE group are formed with varying CCE's. Bythis means, even in a case where PDCCH's of different CCE aggregationsizes in the same UE group are allocated at the same time, it ispossible to prevent a case where PDCCH's of smaller aggregation sizescannot be allocated. Therefore, according to the present embodiment, asin Embodiment 1, it is possible to prevent resource allocation in UEgroups from being limited.

Further, with the present embodiment, the number of CCE's forming searchspaces is the same between all CCE aggregation sizes (e.g. eight CCE'sin FIG. 9), so that it is not necessary to set parameters on a per CCEaggregation size basis. Therefore, according to the present embodiment,it is possible to simplify the system.

Also, as shown in FIG. 10, it is equally possible to separately arrangethe search space of each CCE aggregation size for each UE group over CCE#0 to CCE #31. That is, as shown in FIG. 10, search spaces of differentCCE aggregation sizes in the same UE group are each formed with eightCCE's separately arranged over CCE #0 to CCE #31. Here, as in allocatingmethod 2 of Embodiment 1, in the same UE group, search spaces of asmaller CCE aggregation size are formed with CCE's included in each of aplurality of varying search spaces of a larger CCE aggregation size. Bythis means, even in a case where it is not possible to use one searchspace, it is possible to use other search spaces, so that it is possibleto prevent resource allocation from being limited. By this means, it ispossible to provide the same advantage as in the present embodiment andprovide the same advantage as in allocating method 2 of Embodiment 1.

Embodiments of the present invention have been described above.

Also, a mobile station may be referred to as “terminal station,” “UE,”“MT,” “MS” or “STA (STAtion)”. Also, a base station may be referred toas “Node B,” “BS” or “AP.” Also, a subcarrier may be referred to as“tone,” Also, a CP may be referred to as “GI (Guard interval)”. Also, aCCE number may be referred to as “CCE index.”

Also, all mobile stations or a plurality of mobile stations in a cellneed to receive, for example, a PDCCH used to report resource allocationfor transmitting control channels such as a D-BCH (Dynamic-BroadcastChannel) in which broadcast information is transmitted and a PCH (PagingCHannel) in which paging information is transmitted. That is, thesecontrol channels need to be reported up to mobile stations near the celledge, and, consequently, allocation of a PDCCH of a CCE aggregation sizeof 8 is possible. Therefore, by applying the present invention, even inthe case of using a D-BCH or PCH (of a CCE aggregation size of 8), it ispossible to allocate PDCCH's of other CCE aggregation sizes to specificsearch spaces, without limiting resource allocation.

Also, the error detecting method is not limited to CRC check.

Also, a method of performing conversion between the frequency domain andthe time domain is not limited to the IFFT and FFT.

Also, although cases have been described with the above embodimentswhere signals are transmitted using OFDM as a downlink transmissionscheme and SC-FDMA as an uplink transmission scheme, the presentinvention is equally applicable to eases where transmission schemesother than OFDM and SC-FDMA are used.

Although example cases have been described with the above embodimentswhere the present invention is implemented with hardware, the presentinvention can be implemented with software.

Furthermore, each function block employed in the description of each ofthe aforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSI's, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (FieldProgrammable Gate Array) or a reconfigurable processor where connectionsand settings of circuit cells in an LSI can be reconfigured is alsopossible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

The disclosure of Japanese Patent Application No. 2008-000196, filed onJan. 4, 2008, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is applicable to, for example, mobilecommunication systems.

The invention claimed is:
 1. A radio communication base stationapparatus comprising: processing circuitry configured to allocate acontrol channel to one or more control channel element(s) (CCE(s)) in asearch space, which is comprised of a plurality of CCEs associated withan aggregation size of the one or more CCE(s) and a user equipment (UE)group, wherein: a plurality of UEs are grouped into UE groups, thesearch space is a CCE field subject to blind decoding by each of theplurality of UEs, control channels for different UEs are allocated todifferent CCEs in the search space, and the search space is shared bymore of the UE groups when the aggregation size is larger; and atransmitter configured to transmit the allocated control channel.
 2. Theradio communication base station apparatus according to claim 1, whereinthe search space is comprised of more CCEs when the aggregation size islarger.
 3. The radio communication base station apparatus according toclaim 1, wherein a search space associated with a largest aggregationsize is shared by all of the UE groups, and a search space associatedwith a smallest aggregation size varies between the UE groups.
 4. Theradio communication base station apparatus according to claim 1, whereina search space associated with a smaller aggregation size is comprisedof CCEs, of which at least two search spaces associated with a largeraggregation size are comprised.
 5. The radio communication base stationapparatus according to claim 1, wherein a search space associated with asame UE group and respectively associated with different aggregationsizes are comprised of CCEs different from each of the search spaces. 6.The radio communication base station apparatus according to claim 1,wherein search spaces are comprised of less CCEs when the aggregationsize is smaller.
 7. The radio communication base station apparatusaccording to claim 1, wherein the allocating section allocates thecontrol channel to the one or more CCE(s) in a specific search spaceamong a plurality of search spaces, the specific search space beingassociated with the aggregation size of the control channel and the UEgroup of the control channel, and each of the one or more CCE(s)comprising the plurality of search spaces is shared by more of the UEgroups when the aggregation size is larger.
 8. A radio communicationmobile station apparatus comprising: a receiver configured to receive acontrol channel which is allocated to one or more control channelelement(s) (CCE(s)) in a specific search space, which is comprised of aplurality of CCEs associated with an aggregation size of the one or moreCCE(s) and a user equipment (UE) group, wherein: a plurality of UEs aregrouped into UE groups, the search space is a CCE field subject to blinddecoding by each of the plurality of UEs, control channels for differentUEs are allocated to different CCEs in the search space, and the searchspace is shared by more of the UE groups when the aggregation size islarger; and a decoder configured to decode the control channel in thesearch space.
 9. A control channel allocating method performed by aradio communication base station apparatus comprising: allocating acontrol channel to one or more control channel element(s) (CCE(s)) in asearch space, which is comprised of a plurality of CCEs associated withan aggregation size of the one or more CCEs and a user equipment (UE)group, wherein: a plurality of UEs are grouped into UE groups, thesearch space is a CCE field subject to blind decoding by each of theplurality of UEs, control channels for different UEs are allocated todifferent CCEs in the search space, and the search space is shared bymore of the UE groups when the aggregation size is larger.